Many electronic systems and applications measure voltage levels of electrical signals for various purposes. Various electronic circuits often measure the voltage levels of external electrical signals as inputs. In many cases the measured electrical signal is filtered, amplified, or otherwise modified to conform to the operational parameters of the electronic system measuring the signal. In one typical use, analog to digital converters generate a discrete digital encoding that corresponds to measured analog voltage. Once converted, the digital representation of the analog signal is available for use in a wide variety of microelectronic devices. In many cases, an intermediate voltage sensing circuit transforms the electrical signal to improve the accuracy of the analog to digital converter.
Practical implementations of voltage sensing circuits face several challenges to accurate measurement of electrical signals, particularly time varying signals. Some sources of error include offset errors, noise in the source signal and noise introduced by the voltage sensing circuit, aliasing, and gain errors. Some of these errors, such as offset and gain errors, may increase in magnitude over time.
One method of improving the accuracy of voltage sensing circuits is to modulate the electrical signal being measured, and then to demodulate the signal using a voltage to current converter. In particular, modulation and demodulation with “chopped” signals known to the art provides anti-aliasing, filtering, and sampling of the input signal. However, while this technique provides advantages, the voltage to current converter used in the demodulation process remains susceptible to gain drift over time. This drift may result in incremental errors in voltage sensing that have negative effects on circuits and electronic devices measuring electrical signals. Thus, voltage sensing circuits with improved accuracy are desirable.